Izvestiya, Physics of the Solid Earth最新文献

Abstract—We present the results of magneto-mineralogical and paleomagnetic studies of the Pavlovsk quarry Middle and Upper Devonian section located in the Central Devonian Field (CDF) of the East European Platform. The studied deposits have a complex magnetic mineral composition, with up to 4–6 magnetic phases recorded. The section is subdivided into several zones based on magnetic mineralogy and observed characteristic components of natural remanent magnetization, but the boundaries of the zones do not coincide. Two interpretable characteristic components have been identified in the section, the bipolar Devonian component DE + DW_rev and the anomalous component S_1-2-3-4, whose paleomagnetic poles are consistent with those of several Devonian sections of the East European Platform.

The article presents a prototype of an early warning system for earthquakes for Kyrgyzstan and Uzbekistan. Since large, densely populated cities are located in the seismically active zones of these republics, and there are large hydroelectric power stations and reservoirs, timely warning of emergency services about earthquakes is extremely important. Modeling was carried out for the territory of Kyrgyzstan and Uzbekistan to assess the efficiency of using the seismic networks of these countries for an early warning system. It was shown that for most of the region, an earthquake warning with a time reserve of several tens of seconds is possible. As a result, in 2023, the Central-Asian Institute for Applied Geosciences (CAIAG) developed an early warning system for earthquakes SES (in the Kyrgyz language—Seismikalyk Eskertuu Sistemasy) based on the ACROSS network of strong motion seismic stations (Kyrgyzstan) and the Emergency Situations Ministry of Uzbekistan. The article briefly examines the structure of the system and its operating principles and presents a comparison with its foreign counterpart, the PRESTo system (Italy). The results of the trial operation of the SES demonstrated that its efficiency for the territory of Kyrgyzstan significantly exceeds that of the PRESTo system. The created system is capable of quickly detecting and locating earthquakes on the territory of Kyrgyzstan with magnitudes of 3.5 or higher, as well as reliably identifying earthquakes that occurred outside the network. It was demonstrated that joint work with data from seismic networks of Uzbekistan and Kyrgyzstan could improve the detection of seismic events and determination of their epicenters, mainly at the junction of networks. Currently, the SES is used in the work of emergency services in Kyrgyzstan.

Abstract—The paper presents the results of simultaneous ground-based observations of the gamma-ray spectra from soil radionuclides, the volumetric activity of radon, and the electrical conductivity of the air in the near-surface atmosphere. Based on an analysis of gamma radiation spectra, estimates were obtained for the ²³⁸U, ²³²Th and ⁴⁰K concentrations in the upper soil layer and the dose rate of terrestrial gamma radiation for 43 sites of 8 observation points, the distance between which ranges from 1 m to 25 km. The range of recorded concentrations was 1.28–2.64 mg/kg for ⁴⁰K, 0.7–1.41 mg/kg for ²³⁸U and 4.4–8.88 mg/kg for ²³²Th. The average ratios between the volumetric activities of these soil radionuclides and the statistics of deviations from the average values were determined. During the observation period, the range of variations in the gamma dose rate from soil radionuclides at a height of 1 m above the Earth’s surface was 26–52 nGy/h. During rain, an increase in the number of gamma quanta is recorded in peaks ²¹⁴Bi, reaching 1200% for photon energies near 1765 keV and 300% for photon energies near 2204 keV. The autocorrelation function of the time series of the gamma dose rate from soil radionuclides in fair-weather conditions decreases with a characteristic time scale of several days, which decreases to several hours if precipitation occured during the analyzed time interval, accompanied by an intensification in the ²¹⁴Bi lines in the gamma-ray spectrum. The electrical conductivity of the air in the near-surface atmosphere shows diurnal variation with a minimum during the daytime and two maxima—in the morning and evening. Height-separated observations showed that the electrical conductivity at a height of 0.5 m is, on average, greater than at a height of 1.5 m, and during the daytime, the difference in conductivity values at these heights is expressed more distinctly.

Abstract—The article is devoted to compiling maps of Earth’s gravitational field (EGF) parameters using measurement data from gravimetric equipment, including a plumb line deviation (PLD) meter (astrometer) and a high-precision relative gravimeter. Joint area measurements using the apparatus makes it possible to determine the following EGF parameters: acceleration due to gravity and gravity anomalies, the components and total PLD, and the components of acceleration due to gravity and gravity gradients (second derivatives of the anomalous potential). The total measurement time at a single point using the apparatus does not exceed 1 h, the standard deviation of the PLD component measurement series is from 0.1″ to 0.3″, and acceleration due to gravity is 10 μGal. The paper presents examples of maps of these EGF parameters, compiled from the measurement results using the gravimetric apparatus on the territory of Moscow oblast, including a measurement profile across the Moscow gravity anomaly.

Abstract—In order to prove the synchronicity of magnetization with the formation of rocks of the Neoproterozoic Katav Formation (Southern Urals), a paleomagnetic conglomerate test was performed. Samples of breccias from two sections of the carbonate Katav Formation in the vicinity of Tolparovo and Katav–Ivanovsk were studied. Petrographic and electron microscopic studies of polished sections have been carried out, confirming the proximity of the mineral composition in the fragments and matrix. The qualitative assessment of the randomness of the directions of magnetization of the fragments according to Graham was verified by more stringent Rayleigh and Hodges–Ajne criteria. The results suggest that the conglomerate test is positive, and the high-temperature magnetization component in the rocks of the Katav Formation is primary.

Abstract—Analytical and numerical methods for calculating ground surface displacements in isotropic linear elastic medium with a spherical cavity under excess pressure are compared. The comparison is conducted with varying the depth of the spherical cavity for two ground surface geometries: flat and with conical relief of varying inclinations. In the analytical model, a simplified topography approximation is used. The analysis of the discrepancy between the numerical and analytical solutions suggests the necessity to take into account finite size of the deformation source, especially at shallow depths (less than a kilometer) and to use higher-order terms in the small parameter expansion of the solution for a spherical cavity. For a computational domain with steep conical topography, such as that of the Koryakskii Volcano, Kamchatka Peninsula, the discrepancies between the numerical and analytical solutions are more than 30% for vertical displacement and more than 45% for horizontal component with a source depth of 1450 and 3000 m, respectively. These errors are quite large and significantly exceed the typical error of satellite measurements obtained in favorable conditions. Therefore, using the spherical source model combined with approximate topography representation in regions with steep terrain can lead to significant errors. The discrepancies decrease rapidly as the terrain flattens. The locations of the maxima of the displacement vector components relative to the summit of a conical edifice do not coincide in the analytical solution and in the direct numerical calculation. A simplified consideration of the topography may also give a wrong idea of the position of the deformation source relative to the volcano’s summit.

Abstract—Clustering of acoustic emission pulses was studied on a mechanically preloaded sandstone sample subjected to high-temperature heating. Mechanical loading was performed uniaxially to a load close to failure, with the appearance of surface signs of large cracks. The sample was then heated to 650°C with recording pulses of thermally stimulated acoustic emission (TSAE). Pulses were clustered based on their similarity established by waveform cross-correlation. Three clusters were identified, each containing approximately ten TSAE pulses and potentially corresponding to a specific source, presumably an individual large crack. The distribution of cluster pulses over time and in amplitude during heating is different for each cluster. This may indicate both different activation time and activation threshold of a corresponding crack as well as different rate of crack growth. Separately, a control thermal stimulation experiment was conducted on a sandstone sample without mechanical preloading. No clusters of TSAE pulses were identified for this sample. Additionally, the parameters of TSAE pulses of the identified clusters were analyzed. It is found that the clusters do not form compact, isolated groups in the parameter space, but are distributed against the background of other pulses. The check of the pulses by their parameters based on the physically substantiated criteria has shown that two of the three clusters included several pulses that were inconsistent with the physical features of the experiment. The hierarchical clustering of all TSAE pulses in the parameter space did not reveal groups that have any similarity with the original clusters. The stability of initial cluster identification in the parameter space was tested using decision tree ensemble classification. The third cluster was recognized with the simplest training criteria. The dynamics of pulses of this cluster is most similar to the growth dynamics of a crack activated at a specific heating temperature.

Abstract—This paper is devoted to the study of the features of thermoremanent magnetization (TRM) acquisition in brick fragments from a Roman kiln, uncovered by archeological excavations near the village of Dragovishtitsa (Western Bulgaria), in experiments using the Thellier method as modified by Coe. The aim was to determine the magnitude of the geomagnetic field in ~300 CE. Initially, petromagnetic and archeomagnetic studies were carried out at the paleomagnetic laboratory of the National Institute of Geophysics, Geodesy, and Geography, Bulgarian Academy of Sciences. Then experiments using the Thellier–Coe procedure at two sample cooling rates taking into account the TRM anisotropy were carried out at the laboratory of the main geomagnetic field and petromagnetism of the Schmidt Institute of Physics of the Earth, Russian Academy of Sciences. Based on 18 archaeointensity determinations, the average weighted value of the magnetic field was obtained: B_sр= 56.5 ± 0.8 μT, which corresponds to an archeological age of 260 ± 20 CE. The dating obtained using the archeomagnetic method, 281–342 CE, is consistent with the archeological estimate of the time of operation of the kiln. The calculated archaeointensity satisfactorily corresponds to the reference values of the magnetic field for Bulgaria and confirms its decrease in the time interval ~200–300 CE.

Abstract—Observational data from a receiving station in Petropavlovsk-Kamchatskii were used to analyze variations in very low and low frequency (VLF/LF) radio signals associated with two strong (М ≥ 6.5) earthquakes. The М_w 6.5 earthquake of April 3, 2023 occurred in the Avacha Bay, Pacific coast of the Kamchatka Peninsula; the М_w 7.5 earthquake of January 1, 2024 occurred on the Noto Peninsula, Japan. Disturbances in VLF/LW signals were recorded several days before and during the earthquakes on radio paths from two transmitters intersecting the epicentral zones of the earthquakes. Other factors (magnetic storms, cyclones) that could have caused such disturbances were absent at the time of observations. We believe that anomalies in the behavior of radio signals on both paths were caused by the preparatory processes and occurrence of these earthquakes. An additional argument in favor of this interpretation is the absence of anomalies in signal variations on other radio paths remote from the earthquake sources. Wavelet analysis of the amplitude and phase variations of the nighttime signal bandpass filtered in the range of 0.3–15 mHz has shown that the maximum disturbances in the radio signals corresponded to atmospheric internal gravity wave periods of 10–50 min.

Abstract—It is shown that, according to observations, there was a decrease in the amplitude of four axisymmetric harmonics in the spherical harmonic representation of the geomagnetic field during the last geomagnetic reversal. Only the dipole component changed sign at the time of reversal. For all four modes, on an interval of 200 000 years, quasi variations with characteristic times of 10–50 000 years were observed. During the reversal, magnetic variations with characteristic times of 100–1000 years intensified due to destabilization of hydrodynamic flows in the core.